Go to your sources root directory and do:
#that will recurse subdirectories and list all C files in cscope.files.
#(build the cross reference only, don't compress it, recurse);
#run tceetree with cscope.out as input (default) to get tceetree.out (DOT language representation of function call tree);
#to get a graphical representation of the tree in tceetree.out.png.
There are a lot of options you can specify when invoking dot to customize the graph, for example:
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